ekaterina reguir msc thesis abstract

the carbonatite bodies are confined to the aegirine-microcline fenite aureole in the southern contact zone of the little murun massif with the precambrian crystalline basement.  three mineralogical types of the studied carbonatites are distinguished:  calcite carbonatite (i), ba-sr-ca  carbonatite  (ii), and phlogopite-calcite carbonatite (iii).  in addition, the quartz-feldspar-carbonate rock is classified as a distinct lithological type.  carbonatites of types (i) and (ii) noticeably differ in terms of the composition of rock-forming silicates (potassium feldspar and clinopyroxene) and primary carbonates (sr-rich calcite or barytocalcite, respectively).  in both cases, the primary carbonates underwent complex exsolution processes.  typical exsolution textures are represented by primary carbonates in a core, and the subsolvus mineral assemblage confined to marginal parts of the crystal.  the composition of the primary carbonates becomes progressively depleted in ba + sr (calcite) or sr (barytocalcite) towards the margin, suggesting that interstitial fluid played an important role in the onset of exsolution processes promoting an outward diffusion of components in the peripheral zones of carbonate crystals.  in contrast to the calcite-carbonatite, the phlogopite-calcite carbonatite [type (iii)] is devoid of clinopyroxene and ba-sr-ca carbonates, and rarely exhibits exsolution textures.  potassium feldspar and phlogopite from the carbonatite of type (iii) are ba-rich, and shoe core-to-rim zonation pattern of decreasing ba content.  the mineralogical differences between the carbonatites of types (i) and (iii) clearly indicate that the latter crystallized from a volatile-rich magma depleted in na, under more reducing conditions, and upon crystallization, underwent a rapid loss of residual volatiles.  textural and mineralogical features of the quartz-fledspar-carbonate rock suggest that the rock is transitional from carbonatites to quartz-calcite rocks locally known as "torgolites".